1. Field of the Invention
The present invention relates to dielectric ceramic composition, electronic device and their process of manufacturing and, further in detail, to temperature-compensating dielectric ceramic composition of non-reducing property preferably used for electronic device such as multilayer ceramic capacitor having base metal as internal electrode.
2. Description of the Related Art
Multilayer ceramic capacitor is broadly used as electronic device, and a large number of the multilayer ceramic capacitors is used in an electronic device. Multilayer ceramic capacitor is normally manufactured by stacking the internal electrode layer pastes and dielectric layer pastes with such as sheet method or printing method and thus cofiring.
Dielectric ceramic material used such as for conventional multilayer ceramic capacitor, when firing in the atmosphere of reducing property, has a property of being reduced and semiconductorized. Therefore, as internal electrode material, metals such as Pd which does not melt at the sintering temperature of dielectric ceramic material and also does not become oxidized even when firing under high oxygen pressure which does not semiconductorize the dielectric ceramic material was used.
However, metals such as Pd are precious that it is a major obstacle for attempt to reduce the price of multilayer ceramic capacitor. Therefore, as internal electrode material, the use of relatively low priced base metal of Ni or Ni-alloys are becoming to be the mainstream.
On the contrary, when using the base metal as conductive material of internal electrode layer, firing in an atmosphere leads to the oxidation of the internal electrode. Therefore, dielectric layer and internal electrode layer need to be cofired in reducing atmosphere.
But when fired in reducing atmosphere, dielectric layer is reduced and insulation resistance is lowered. Therefore, dielectric material of non-reducing property is provided. For instance, dielectric ceramic compositions of Mg—Ti—O series have excellent temperature characteristic of dielectric constant and widely used for temperature-compensating ceramic capacitor.
However, these dielectric ceramic compositions of Mg—Ti—O series, when fired under reducing atmosphere, are reported to be reduced and semiconductorized to have a remarkable property of reducing resistance (See non-patent article 1: Journal of the Ceramic Society of Japan 100 [10] 1992, “Phase-Fine structure change of MgTiO3 ceramics by treatment in reduction”). Moreover, dielectric ceramic compositions of Mg—Ti—O series, for deposit of Ti-rich heterogeneous phase (Acicular crystal) while sintering, are considered to be difficult for composition control.
Further, The Patent Article 1: The Japanese Unexamined Patent Publication No. 11-240753, The Patent Article 2: The Japanese Unexamined Patent Publication No. 11-278925 and The Patent Article 3: The Japanese Unexamined Patent Publication No. 8-45348 disclose dielectric ceramic composition mainly comprising MgTiO3. However, dielectric ceramic compositions as in The Patent Articles 1 to 3 were not dielectric ceramic composition of non-reducing property that can apply to Ni internal electrode.
The present invention has been made in consideration with the above circumstances and has an object to provide dielectric ceramic composition of non-reducing property preferably used for multilayer ceramic capacitor having base metal, such as Ni, as internal electrode which is hard to reduce resistance even firing in reduced atmosphere and has high relative dielectric constant and small amount of dielectric loss.